A metal-air battery has a high energy density and, therefore, is noted as a next-generation battery. The metal-air battery generates electricity, where a fuel electrode containing an electrode active material serving as a fuel is used as an anode and an air electrode is used as a cathode.
A zinc-air battery, in which metal zinc serves as an electrode active material, is mentioned as a typical example of the metal-air batteries. As for the zinc-air battery, it is considered that an electrode reaction represented by Chemical formula 1, as described below, proceeds in the cathode.O2+2H2O+4e−→4OH−  (Chemical formula 1)Meanwhile, it is considered that electrode reactions represented by Chemical formulae 2 and 3, as described below, proceed in the anode.Zn+4OH−→Zn(OH)42−+2e−  (Chemical formula 2)Zn(OH)42−→ZnO+2OH−+H2O  (Chemical formula 3)
As such reactions proceed, the electrode active material in the fuel electrode is consumed. Therefore, the metal-air battery has a structure in which the fuel electrode can be exchanged to supply a metal serving as the electrode active material (for example, refer to PTL 1).
Also, the metal-air battery is provided with a plurality of electrochemical cells connected in series or connected in parallel to obtain a large output.